Air tool muffler

ABSTRACT

A pneumatic portable power tool such as an impact wrench is disclosed which incorporates an improved air exhaust passage and muffler. The tool is of the pistol-grip type and the exhaust passage is provided immediately above the trigger and handle, the exhaust air being directed away from the operator. An improved muffler incorporating several noise-reduction features in a simplified construction is provided in the passage.

United States Patent 91 Fleigle 1 3,823,795- 1451 July 16,1974

1 1 AIR TOOL MUFFLER [75] Inventor: Donald Earl Fleigle, Abingdon, Md.

[73] Assignee: The Black and Decker Manufacturing Company, Towson,

22 Filed: May 30, 1973 [21] Appl. No.: 365,199 T 52 us. (:1. ..18l/36A 51 1m. (:1. ..F01n 3/06 [58] Field of Search 181/36 A, 36 D, 36 R, 46, 181/47 R, 56, 57, 60, 63; 173/163, 168, 169

v [56] References Cited UNITED STATES PATENTS 2,073,480 3/1937 Jimmerson.; 181/36 A UX 2,169,359 8/1939 Jones et al. 181/56 2,950,775

8/1960 Zwayer 181/36 A UX 2,966,138 12/1960 Quackenbush 181/36 A UX 3,384,200 5/1968 Baker et al 181/36 A UX FOREIGN PATENTS OR APPLICATIONS 810,398 3/1959 1 Great Britain... l8l/36 A Primary Examiner- -Richard B. Wilkinson Assistant Examiner-John F. Gonzales [57] ABSTRACT A pneumatic portable power tool such as an impact wrench is disclosed which incorporates an improved air exhaust passage and muffler. The tool is of the pistol-griptype and the exhaust passage is provided immediately above the trigger and handle, the exhaust air being directed away from the operator. An improved muffler incorporating several noise-reduction features in a simplified construction is provided in the passage.

- 9 Claims, 6 Drawing Figures PATENTEUJUU 61974 FIG. 4

FIG. 3

AIR TOOL MUFFLER BACKGROUND OF THE INVENTION The present invention is directed to portable power tools of the pneumatic type and is specifically directed to tools of the pistol grip type wherein the motor and output shaft are substantially aligned and the operator handle extends perpendicularly therefrom.

Pneumatic power tools offer many advantages to industrial and commercial users in terms of power-toweight ratios and efficiency. However, a major disadvantage of such tools has been the high noise level generated during operation. The noise produced by such tools is the inherent result of allowing high velocity air to exhaust from the tool into the atmosphere without significant provision for m'uffling.

While various techniques for reducing these noise levels are well known in principle, it has been difficult or impossible to adapt these principles to the power tool field. One factor is this situation has been the difficulty of providing small, compact but effective muffling capability which can be built into a portable power tool; in addition, users have been reluctant to pay the price in terms of either lostefficiencyor increased dollar cost or both. It is the purpose of this invention to provide a simplified muffled exhaust arrangement for portable power tools which combines small size with effective noise reduction without sacrificing either efficiency or price.

OBJECTS OF THIS INVENTION BROAD STATEMENT OF THE INVENTION In accord with one embodiment of this invention, an improved pneumatic power tool is provided which includes a rotary motor adapted to be connected to a source of pressurized fluid and an output device driven by the motor. ln one specific form, the power tool may comprise an impact wrench with a generallyaxially aligned motor and output shaft and a handle extending at an angle thereto. The handle includes an inlet path controlled by a trigger member. Fluid is exhausted from the motor into a region formed within the tool housing. In accord with the present invention, the region is subdivided into two separate chambers by an intermediate barrier having a plurality of small apertures therein. The fluid passes from one of these chambers through the apertures into the other and then is exhausted into the atmosphere through a further wall also provided with small apertures. This system effectively reduces the noise of the exhaust stream without interfering with the efficiency of the motor.

Preferably, the exhaust stream is passed through two expansion chambers and through two diffusionbarriers to reduce the noise. In a particular embodiment, these .44 of FIG. 3;

multiple muffling elements are formed by a separate muffler subassembly which is inserted and mounted within a large chamber formed in the tool housing.

In the figures, FIG. 1 is a side elevation, partially broken away, of a portable pneumatic power tool in accord with the present invention;

FIG. 2 is a front elevation of the tool of FIG. 1;

FIG. 3 is an enlarged front elevation of a section of FIG. 2;

FIG. 4 is a cross sectional view taken along the lines FIG. 5 is a perspective view, partially broken away, of the muffler insert of FIG; 4; and

FIG. 6 is a rear perspective view of the insert of FIG. 4.

In FIG. 1, a portable pneumatic impact wrench 10 is shown by way of illustration. In accord with conventional practice, the wrench includes an inlet bushing 11 for receiving a supply hose from a source of compressed air, a handle 12 through which the inlet air passes and a trigger 13 which controls the flow of air to the tool. The tool further includes an air motor comprising a rotor and a plurality of vanes such as that shown at 14 which is adapted to be driven by the compressed air and which is coupled via a shaft and a suitable impact mechanism to an output member 15.

After the compressed air passes through the motor, rotating it and producing an output torque, the air stream must be exhausted to the atmosphere. This exhaust stream can produce noise which is irritating or even physically harmful unless suitable muffling is provided. In accord with the present invention, the air stream leaving the motor vanes l4 passes through an aperture 16 into a chamber 17. Since the tool housing is conventionally a metal casting, the chamber 17 may be formed at the time of casting the overall housing. In order to define the muffling arrangement, a muffler insert 20 is provided within the chamber 17. The muffling insert, which can be seen in the frontal view of FIG. 2, preferably comprises a separately formed subassembly which is inserted during manufacture of the tool and which may be retained in place by a screw 21.

FIGS. 3, 4 and 5 illustrate the muffling insert 20 more clearly. Specifically, this insert comprises a molded plastic cartridge provided at the time of molding with a back wall 22 and side walls 23 defining an intermediate expansion chamber and a separately molded front wall 24 which is suitably .affixed to the cartridge. The assembly is provided with an aperture 25 for receiving the screw 21. In the particular case illustrated, the rear of the cartridge is shaped as shown at 26 to fit over a housing boss 27 which includes a threaded aperture for receiving the screw 21.

The combination of the muffiing insert 20 and chamber 17 provides a simple and easily manufactured muffiing arrangement which actually embodies several desirable noise-reducing features. For example, the two expansion chambers, one of which is formed by the chamber 17 and the back wall 22 of the cartridge and the other which is formed internally of the cartridge between its back wall 2 and front wall 24, are sized so as to attenuate at overlapping noise frequency bands and thus reduce the volume of noise generated at those frequencies. As a second feature, the walls 22 and 24 of the muffiing insert are provided with a large number of small holes 28. In each case, the air passing through these walls is formed into a plurality of small jets. This 3 greatly increases the boundary area between the jets entering the downstream region and the air in that region. The noise generated by a jet of air passing through an aperture has been found to be inversely proportional to the boundary area and thus, the provision of these walls with multiple apertures substantially reduces the noise generated. A further element of this system is the relative pressure ratios across each of these walls. If the downstream pressure is too low relative to the upstream pressure, the flow through the apertures may reach sonic velocities which causes a sub-,

stantial increase in the amount of sound generated. In

accord with the arrangement illustrated, this possibility which they are located.

As previously noted, it is desirable to provide a'plurality of small apertures rather than one or a few large apertures in order to distribute the interface between air flow exiting from the apertures and the downstream body of air. However, it has alsobeen found to be necessary to maintain the diameter of the apertures sufficiently large so that the effective cross sectional area of the air flow through the apertures is not unduly restricted. Specifically, in the illustrated structure, the

back wall 22 has a thickness of about 0.10'inch and-the diameter-of the holes in the back wall is approximately 0.05 inch. The front wall 24 has a thickness of 0.15 inch and the apertures therein are also about 0.05 inch. More generally, it is preferred that the length to diameter ratio of the apertures be between about one-to-one and four-to-one. The number of apertures, of course, is large enough so that the air flow out of the motor is not seriously restricted. This structure will provide maximum air flow with minimum noise generation.

While a specific embodiment of the present invention has been illustrated and described in the foregoing drawings and specification, it will be evident to those skilled in the art that many changes and modifications therein can be made without departing from the essential teachings of the invention. Accordingly, it is intended that the amendedclaims cover all such changes and modifications as fall within the true spirit and scope of this invention. 1

lclaim:

1. A portable pneumatic power tool comprising a housing; a rotary air motor enclosed within said housing; a handle portion extending from said housing; ex-

haust passage means for air flow exhausting from said motor between said handle portion and said air motor, said exhaust passage means comprising a first attenuation chamber in the path of said air flow; a second attenuation chamber also in the path of said air flow; a first apertured wall separating and partially defining said first and second chambers; and a second apertured wall at the interface between said second chamber and atmosphere.

2. A portable pneumatic power tool as claimed in claim 1 wherein said motor rotates about an axis; wherein said handle extends at a substantially right angle tothe axis of said motor; and wherein said exhaust passage means extends in a direction substan- 4 i tially parallel to that of said motor axis to direct exhausting air away from an operator of said tool.

3. A portable pneumatic power tool as claimed in claim 2 wherein said housing comprises a cast body including a tubular portion enclosing said motor; wherein said exhaust passage means comprises a cavity in said cast body, said cavity extending along one side of said tubular portion; and wherein said handle extends outwardly from said housing at said cavity.

4. A portable pneumatic power tool as claimed in claim 1 wherein said apertures in said first apertured wall have a length to diameter ratio in the range of from one-to-one to four-to-one.

5. A portable pneumatic power tool as claimed in claim 4 wherein said apertures in said second apertured wall have a length to diameter ratio in the range of from one-to-one to four-to-one.

,6. A portable pneumatic power tool comprising a housing; a rotary air motor enclosed within saidhousing;air inlet passage means for providing a supply of pressurized air tosaid motor; handlemeans extending at one side of said motor; and exhaust passage means for air exhaustingfrom said motor, said exhaust passage means comprising a cavity in said housing betweensaid motor and said handle and including a first attenuation chamber sized to further reduce the sound intensity of air exhausting from said motor, a first apertured wall, a second attenuation chamber sized to further re- I duce the sound intensity of air exhausting from said motor, and a second apertured wall, said second wall lying between said second chamber and the atmosphere.

7. A portable pneumatic power tool as claimed in claim 6 wherein said exhaust passage directs air forwardly of said handle away from an operator holding said tool.

8. A portable pneumatic power tool'comprising a housing; a rotary air motor enclosed within said housing; a handle portion extending to one side from said housing; exhaust passage means for air flow exhausting from said motor between saidhandle portion and said air motor, said exhaust passage means comprising a first chamber in the-path of said air flow; a second chamber also in the path of said airflow; a first aper-. tured wall separating and partially defining said first and second chambers; and a second apertured wall at the interface between said second chamber and atmo sphere; said first and second chambers being sized to prevent noise generation upon passage of exhaust air therethrough and said apertures in said first and said second walls having a length-to-effective diameter ratio in the range of from one-to-one to four-to-one.

9. A portable pneumatic power tool comprising a housing; an air motor enclosed within said housing; air inlet passage means for providing a supply of pressurized air to said motor; and exhaust passage means com prising a cavity in said housing for air exhausting from said motor, said exhaust passage means defining a first 

1. A portable pneumatic power tool comprising a housing; a rotary air motor enclosed within said housing; a handle portion extending from said housing; exhaust passage means for air flow exhausting from said motor between said handle portion and said air motor, said exhaust passage means comprising a first attenuation chamber in the path of said air flow; a second attenuation chamber also in the path of said air flow; a first apertured wall separating and partially defining said first and second chambers; and a second apertured wall at the interface between said second chamber and atmosphere.
 2. A portable pneumatic power tool as claimed in claim 1 wherein said motor rotates about an axis; wherein said handle extends at a substantially right angle to the axis of said motor; and wherein said exhaust passage means extends in a direction substantially parallel to that of said motor axis to direct exhausting air away from an operator of said tool.
 3. A portable pneumatic power tool as claimed in claim 2 wherein said housing comprises a cast body including a tubular portion enclosing said motor; wherein said exhaust passage means comprises a cavity in said cast body, said cavity extending along one side of said tubular portion; and wherein said handle extends outwardly from said housing at said cavity.
 4. A portable pneumatic power tool as claimed in claim 1 wherein said apertures in said first apertured wall have a length to diameter ratio in the range of from one-to-one to four-to-one.
 5. A portable pneumatic power tool as claimed in claim 4 wherein said apertures in said second apertured wall have a length to diameter ratio in the range of from one-to-one to FOUR-TO-ONE.
 6. A portable pneumatic power tool comprising a housing; a rotary air motor enclosed within said housing; air inlet passage means for providing a supply of pressurized air to said motor; handle means extending at one side of said motor; and exhaust passage means for air exhausting from said motor, said exhaust passage means comprising a cavity in said housing between said motor and said handle and including a first attenuation chamber sized to further reduce the sound intensity of air exhausting from said motor, a first apertured wall, a second attenuation chamber sized to further reduce the sound intensity of air exhausting from said motor, and a second apertured wall, said second wall lying between said second chamber and the atmosphere.
 7. A portable pneumatic power tool as claimed in claim 6 wherein said exhaust passage directs air forwardly of said handle away from an operator holding said tool.
 8. A portable pneumatic power tool comprising a housing; a rotary air motor enclosed within said housing; a handle portion extending to one side from said housing; exhaust passage means for air flow exhausting from said motor between said handle portion and said air motor, said exhaust passage means comprising a first chamber in the path of said air flow; a second chamber also in the path of said air flow; a first apertured wall separating and partially defining said first and second chambers; and a second apertured wall at the interface between said second chamber and atmosphere; said first and second chambers being sized to prevent noise generation upon passage of exhaust air therethrough and said apertures in said first and said second walls having a length-to-effective diameter ratio in the range of from one-to-one to four-to-one.
 9. A portable pneumatic power tool comprising a housing; an air motor enclosed within said housing; air inlet passage means for providing a supply of pressurized air to said motor; and exhaust passage means comprising a cavity in said housing for air exhausting from said motor, said exhaust passage means defining a first expansion chamber adapted to reduce the sound intensity of said exhausting air; an insert mounted in one end of said cavity, said insert comprising first and second apertured walls and a plurality of side walls defining a second expansion chamber adapted to further reduce the sound intensity of said exhausting air; said first apertured wall being disposed between said first and said second chambers, and said second apertured wall being disposed at the interface between said second expansion chamber and the surrounding atmosphere. 